Cooling unit

ABSTRACT

The invention relates to a cooling unit for cooling a load having a refrigeration circuit, at least one compressor for compressing a refrigerant that circulates in the refrigeration circuit, several heat exchangers, in which the refrigerant is cooled against itself, and two expansion devices that operate at different temperature levels, in which, at least temporarily, at least one partial stream of the refrigerant is expanded to produce cold. At least one additional expansion device is provided. The latter is connected to the refrigeration circuit in such a way that the refrigerant that can be, at least temporarily, at least partially expanded in the additional expansion device to produce cold.

SUMMARY OF THE INVENTION

The invention relates to a cooling unit, comprising

-   -   a refrigeration circuit,     -   at least one compressor, which uses the compression of the         refrigerant that circulates in the refrigeration circuit,     -   several heat exchangers, in which the refrigerant is cooled         against itself, and     -   two expansion devices that operate at different temperature         levels, in which, at least temporarily, at least one partial         stream of the refrigerant is expanded to produce cold.

The invention also relates to a method for operating a cooling unit.

A general cooling unit as well as a general method for operating a cooling unit are known, for example, from the un-prepublished German Patent Application 102011009965.

General cooling units are usually used for cooling or heating cryogenic loads, such as, for example, superconducting magnets, wherein the so-called Claude process is used. The cooling is normally carried out at a temperature from ambient temperature to 5 K. The Claude process is designed for a defined cooling temperature. If cooling at another temperature level is now required, such as, for example, during the controlled cooling or heating of superconducting magnets, the flow cross-sections are largely specified within the cold-generating expansion stages. This has the result that the available compressor mass flow can be used only partially in these expansion stages. During such a time period, the installed power capacity is thus available for cold generation to only a limited extent.

To eliminate this problem, approaches were already implemented in which the non-usable compressor mass flow is cooled by means of an auxiliary refrigerant—usually liquid nitrogen—via additional heat exchangers and is tempered via a mixing section before it supports the cooling of the load. In this connection, however, it is disadvantageous that the use of the entire compressor mass flow is possible only by an additional consumption of auxiliary refrigerant.

An object of the invention is to provide a cooling unit, as well as a method for operating a cooling unit, wherein at essentially each temperature level it is possible to use the entire compressor mass flow, without having to provide an auxiliary refrigerant.

Upon further study of the specification and appended claims, other objects and advantages of the invention will become apparent.

To achieve these objects, a cooling unit is provided, which is characterized in that at least one additional expansion device is provided, whereby the latter is incorporated into the refrigeration circuit in such a way, after the load is cooled, that the refrigerant that circulates in the refrigeration circuit can be, at least temporarily, at least partially expanded in the additional expansion device to produce cold.

The method according to the invention for operating a cooling unit is characterized in that the compressor mass flow is divided and sent to three expansion devices during the cooling and/or heating procedure in such a way that essentially at any time, the entire compressor mass flow serves to cool the load that is to be cooled.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated schematically with reference to an exemplary embodiment in the drawing and will be described extensively hereinafter with reference to the drawing. Various other features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawing wherein:

the FIGURE illustrates an exemplary embodiment of the invention.

The cooling unit according to the invention, the method according to the invention for operating a cooling unit, as well as other advantageous configurations of the same are explained in more detail below based on the embodiment depicted in the FIGURE.

The cooling unit depicted in the FIGURE has several heat exchangers HX1 to HX6, a separator D, several valves V1 to V9, as well as three expansion devices TU1 to TU3. Below, the cooling and heating procedures of a cryogenic load, which is to be cooled by means of the cooling unit according to the invention, are explained in more detail.

At the beginning of the cooling procedure, the temperature of the cryogenic load that is to be cooled is approximately 300 K. Via the line 1, the refrigerant, compressed to the desired circulation pressure by means of a compressor (not shown), is fed to the first heat exchanger HX1. With the regulating valve V7 opened, a partial stream of the refrigerant is fed via the line sections 1, 2 and 3 to the load that is to be cooled. The heated refrigerant is removed from the load that is to be cooled via the line 4 with the regulating valve C9 opened. After cooling in the heat exchanger HX2, the refrigerant is fed via the line sections 4′, 20 and 21 to the expansion device TU3 and expanded in the latter to produce cold.

Then, the expanded partial refrigerant stream flows through line sections 22, 6 and 7, passing through heat exchangers HX4 TO HX1, before being delivered to the compressor or the compressor unit of the cooling unit according to the invention.

A partial stream of the refrigerant that is fed to the load that is to be cooled is fed via line 13, with a regulating valve V2 opened, to the second expansion device TU2, expanded in the latter to produce cold, and then, via the line sections 14 and 15, combined with the refrigerant stream, removed from the load that is to be cooled, in line section 4′. The heat exchanger HX3 has a bypass line 12, in which a regulating valve V4 is arranged. By means of the two regulating valves V2 and V4, the inlet temperature of the expansion device TU2 can be regulated.

The refrigerant stream that is not fed to the expansion device TU3 is expanded to a low pressure via the line 5, in which a regulating valve V5 is arranged, and mixed into the refrigerant stream in the line 6. As return temperature (i.e., the temperature of the stream fed to the compressor) drops, the flow through the valve V5 continually decreases until it stops entirely.

At the same time, the first expansion device TU1 is turned on and is fed more power as return temperature drops. To this end, a portion of the compressed refrigerant stream is fed via line 10, in which a regulating valve V1 is arranged, to the expansion device TU1. After expansion in expansion device TU1, the refrigerant is combined, via line 11, with the refrigerant stream that is fed to the expansion device TU3.

During this cooling phase, quantitatively small partial refrigerant streams are permanently fed via the slightly opened valves V6 and V8 to the heat exchangers HX6 and HX5 in order to cool the latter simultaneously.

By means of the previously described procedure, the load that is to be cooled can be cooled to a temperature of approximately 100 K. In order to achieve additional cooling to a temperature of approximately 30 K, the regulating valves V7 and V9 are closed, while the regulating valves V6 and V8 are further opened.

The refrigerant that is to be fed to the load to be cooled is now divided into two partial streams. The first partial stream is delivered to the first expansion device TU1 and then fed, via the line sections 10, 11, 20, 15, and 40, to the load that is to be cooled. The second refrigerant stream is fed via the second expansion device TU2 and thus via the line sections 2, 13, 14 and 40 to the load that is to be cooled. During the cooling process, the mass stream that is fed to the third expansion device TU3 is successively reduced until the expansion device TU3 is fed exclusively from the expansion device TU1 that is placed upstream therefrom.

To implement the last stage of the cooling procedure—wherein, e.g., a cooling of the load to a temperature of approximately 5 K is performed—the third expansion device TU3 is throttled more and more as return temperature drops and is finally stopped. The compressor mass flow now flows to the load to be cooled exclusively via the two expansion devices TU1 and TU2, which now operate in parallel, but at different temperature levels. The refrigerant that flows back from the load that is to be cooled is expanded via V8 and sent to phase separator D. By the Joule-Thomson Effect that occurs at this temperature, it is cooled once more and partially liquefied. The liquefied refrigerant is guided over line section 32 through the heat exchanger HX6 and evaporated therein by countercurrent heat exchange. The vapor portion from phase separator D is delivered via line section 31 directly to the heat exchanger HX5.

During the heating procedure, the previously described course of the process is performed in reverse sequence.

As can be seen from the previously described process, the entire compressor mass flow is completely available for cooling in each phase of the cooling and heating procedure.

Relative to a general cooling unit, as it is described in, for example, the above-mentioned German Patent Application 102011009965, the cooling unit according to the invention has at least three additional process lines including related valves. As a result, a distribution of the remaining compressor mass flow is made possible, which makes it possible, at any point, to draw on the entire compressor mass flow for cooling the cryogenic load.

By means of the cooling unit according to the invention or the process of using the cooling unit, the entire compressor mass flow can now be used for cold generation. The cooling unit according to the invention thus reaches a maximum level of efficiency during the operation of the cooling and heating procedures of the cryogenic load. The previously required use of an additional auxiliary refrigerant thus becomes unnecessary.

The entire disclosure[s] of all applications, patents and publications, cited herein and of corresponding German Application No. DE 10 2011 013 345.3, filed Mar. 8, 2011 are incorporated by reference herein.

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples. 

1. A cooling unit for cooling a load, said cooling unit comprising a refrigeration circuit, which comprises: at least one compressor which compresses the refrigerant that circulates in the refrigeration circuit, a plurality of heat exchangers (HX1-HX6), wherein the refrigerant is cooled against itself, and two expansion devices (TU1, TU2) that operate at different temperature levels, in which, at least temporarily, at least one partial stream of the refrigerant is expanded to produce cold, and at least one additional expansion device (TU3) is connected to the refrigeration circuit in such a way that the refrigerant that circulates in the refrigeration circuit, after the load is cooled, can be, at least temporarily, at least partially expanded in the additional expansion device (TU3) to produce cold.
 2. A method for operating a cooling unit according to claim 1, wherein, during the cooling and/or heating procedure, the compressor mass flow is divided into partial streams and sent to the three expansion devices (TU1, TU2, TU3) in such a way that essentially at any time, the entire compressor mass flow serves to cool the load that is to be cooled.
 3. A method according to claim 2, wherein the cooling unit is used to cool a cryogenic load.
 4. A method according to claim 3, wherein the cooling unit is used to cool a superconducting magnet. 